The present invention relates generally to a system and method for sensing and controlling characteristics of certain internal combustion engines, and particularly to a system and method for improving the sensing of exhaust backpressure for an engine.
Internal combustion engines are used in a wide variety of applications, including the providing the power for a variety of vehicles. Generally, such engines include one or more cylinders that each contain a piston designed for movement in a reciprocating manner. Each piston is connected to a crankshaft by a connecting rod that delivers force from the piston to the crankshaft in a manner that rotates the crankshaft. Power to drive the piston is provided by igniting an air-fuel mixture supplied to the cylinder on a side of the piston opposite the connecting rod. The air-fuel mixture is ignited, e.g. by an ignition device, such as a spark plug having electrodes across which a spark is provided.
Air and fuel may be supplied to each cylinder by a variety of mechanisms, such as carburetor or fuel injection systems. Adjusting or changing the air-fuel mixture according to operating conditions permits greater optimization of desired engine operation characteristics. For example, application of greater throttle for increased engine speed requires a greater quantity of fuel. On the other hand, maintaining the engine operation at a lower RPM, requires a lesser quantity of fuel supplied to each cylinder. Generally, greater control over combustion conditions, e.g. air-fuel mixture, provides an engine designer with a greater ability to bring about a desired engine performance under a greater range of operating conditions.
Modern engines often utilize electronic fuel injection systems that inject specific amounts of fuel based on a stored fuel map. The fuel map effectively acts as a guide to fuel injection quantities based on a variety of sensed parameters, such as engine speed, throttle position, exhaust pressure and engine temperature. For example, detection of pressure in the exhaust system under given operating conditions can be used to adjust one or more combustion parameters of the engine.
Pressure sensors can be used to detect pressure in an exhaust system and to output a signal representative of the pressure. However, the exhaust pressure is subject to large fluctuations that create a sometimes radically fluctuating output signal. Often, it is desirable to obtain a more useable signal that is representative of the average exhaust backpressure of the engine.
The present invention features a system and method for measuring the exhaust pressure of an internal combustion engine. The technique utilizes a pressure sensor placed into fluid communication with an exhaust flow path of the internal combustion engine. Additionally, an attenuator is utilized to automatically provide time averaging of the otherwise relatively large exhaust pressure fluctuations.